In North America asphalt shingles are used as the surface elements of many inclined roofs. However other materials are known, such as wooden shakes, such as cedar shakes; clay tiles; and metal roofing panels. In agricultural or industrial applications, relatively long, corrugated metal sheets of constant section, or hat sections have been long known. However, metal or plastic roofing tiles may also be provided in smaller sections, those sections having a stamped contour or texture. The stamped texture may be intended to simulate the pattern of, for example, asphalt shingles. Alternatively, they may have a pattern resembling slates or tiles. In a further alternative, they may have the general appearance of wooden shakes, such as cedar shakes.
Another common problem with metal shingles is the issue of the double overlap at one corner. That is, in the installation of metal tiles, not only does the row next above overlap the upper margin of the next lower row, but, in addition, one or other of the next adjacent plates to the left or right also over laps laterally, such that the nailing tab on that side is hidden. The adjacent plates may also have interlocking ridges along their edges to discourage entry of water. There is a tendency at the upper corner of the under-lapping plate for the wind to drive water into the joint, and thus under the adjacent plate. Over time a build up of moisture may occur. This build up of moisture may be more than the underlayment may be suitable for handling.